Dai, P, Lu, W, Le, K & Liu, D 2020, 'Sliding Mode Impedance Control for contact intervention of an I-AUV: Simulation and experimental validation'.
Dai, P & Katupitiya, J 2018, 'Force control for path following of a 4WS4WD vehicle by the integration of PSO and SMC', Vehicle System Dynamics, vol. 56, no. 11, pp. 1682-1716.View/Download from: Publisher's site
Dai, P, Taghia, J, Lam, S & Katupitiya, J 2018, 'Integration of sliding mode based steering control and PSO based drive force control for a 4WS4WD vehicle', Autonomous Robots, vol. 42, no. 3, pp. 553-568.View/Download from: Publisher's site
Tan, Q, Dai, P, Zhang, Z & Katupitiya, J 2018, 'MPC and PSO based control methodology for path tracking of 4WS4WD vehicles', Applied Sciences (Switzerland), vol. 8, no. 6.View/Download from: Publisher's site
© 2018 by the authors. Four wheel steering and four wheel drive (4WS4WD) vehicles are over-actuated systems with superior performance. Considering the control problem caused by the system nonlinearity and over-actuated characteristics of the 4WS4WD vehicle, this paper presents two methods to enable a 4WS4WD vehicle to accurately follow a predefined path as well as its reference trajectories including velocity and acceleration profiles. The methodologies are based on model predictive control (MPC) and particle swarm optimization (PSO), respectively. The MPC method generates the virtual inputs in the upper controller and then allocates the actual inputs in the lower controller using sequential quadratic programming (SQP), whereas the PSO method is proposed as a fully optimization based method for comparison. Both methods achieve optimization of the steering angles and wheel forces for each of four independent wheels simultaneously in real time. Simulation results achieved by two different controllers in following the reference path with varying disturbances are presented. Discussion about two methodologies is provided based on their theoretical analysis and simulation results.
Cong, M, Wen, H, Du, Y & Dai, P 2012, 'Coaxial twin-shaft magnetic fluid seals applied in vacuum wafer-handling robot', Chinese Journal of Mechanical Engineering (English Edition), vol. 25, no. 4, pp. 706-714.View/Download from: Publisher's site
Compared with traditional mechanical seals, magnetic fluid seals have unique characters of high airtightness, minimal friction torque requirements, pollution-free and long life-span, widely used in vacuum robots. With the rapid development of Integrate Circuit (IC), there is a stringent requirement for sealing wafer-handling robots when working in a vacuum environment. The parameters of magnetic fluid seals structure is very important in the vacuum robot design. This paper gives a magnetic fluid seal device for the robot. Firstly, the seal differential pressure formulas of magnetic fluid seal are deduced according to the theory of ferrohydrodynamics, which indicate that the magnetic field gradient in the sealing gap determines the seal capacity of magnetic fluid seal. Secondly, the magnetic analysis model of twin-shaft magnetic fluid seals structure is established. By analyzing the magnetic field distribution of dual magnetic fluid seal, the optimal value ranges of important parameters, including parameters of the permanent magnetic ring, the magnetic pole tooth, the outer shaft, the outer shaft sleeve and the axial relative position of two permanent magnetic rings, which affect the seal differential pressure, are obtained. A wafer-handling robot equipped with coaxial twin-shaft magnetic fluid rotary seals and bellows seal is devised and an optimized twin-shaft magnetic fluid seals experimental platform is built. Test result shows that when the speed of the two rotational shafts ranges from 0-500 r/min, the maximum burst pressure is about 0.24 MPa. Magnetic fluid rotary seals can provide satisfactory performance in the application of wafer-handling robot. The proposed coaxial twin-shaft magnetic fluid rotary seal provides the instruction to design high-speed vacuum robot. © Chinese Mechanical Engineering Society and Springer-Verlag Berlin Heidelberg 2012.
Magnetic fluid seal is a special kind of hermetical device. It seals gas or liquid by the sealing ring which is formed when magnetic fluid is placed in the designed strong magnetic field. Such seal has the advantages of simple design, low friction and zero leakage at almost any rotation speed. For better understanding the principle of magnetic fluid seal, some related knowledge of magnetic fluid is presented. On the basis of that, the principle and structure of typical magnetic fluid seal are introduced. Then, a review of the various types of magnetic fluid seals is presented. Its brief history is also reviewed. This is followed by retrospection of some latest patents and applications in magnetic fluid seals. The patents and applications concern a period extending from the years 2003 up to date. The patents principally concern innovative designs of magnetic fluid seal's structure and arrangement. The applications mentioned in this paper mainly focus on areas of high-tech, such as wafer treatment equipment, weber processing apparatus, immersion lithography, X-ray apparatus, and so on. At last, a description of the future developments expected in magnetic fluid seal is concluded. © 2009 Bentham Science Publishers Ltd.
Dai, P & Katupitiya, J 2015, 'Force control of a 4WS4WD vehicle for path tracking', IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM, pp. 238-243.View/Download from: Publisher's site
© 2015 IEEE. The aim of this paper is to develop a system where forces at the wheels of a ground vehicle are controlled to guide the vehicle along a planned path. The 7-order Bézier curves are applied to path planning and online path tracking, and used to obtain profiles of velocities and accelerations for the guidance of a 4WS4WD vehicle. The dynamic model used for force control is developed for the determination of the reference forces and steering angles at four wheels. The motion profiles obtained using the continuously updated Bézier segments are then applied to control the driving and steering motions of individual wheels. Note that this control methodology does not address the closed loop path tracking control, instead it only demonstrates the resilience of an open loop system through a vehicle design which only requires a dynamic model where the number of uncertain parameters are minimized. In future work, complementary steering control inputs will be generated through close loop path tracking control. Simulation results are provided to validate the proposed methodology.
Dai, P & Katupitiya, J 2015, 'Online path tracking and motion optimization of a 4WS4WD vehicle', IEEE International Conference on Intelligent Robots and Systems, pp. 4133-4139.View/Download from: Publisher's site
© 2015 IEEE. This paper presents a methodology to optimize the drive forces and steering angles for achieving accurate path tracking by a four wheel steer and four wheel drive (4WS4WD) vehicle. The 7-order Bézier curves are applied in path planning and online tracking, and used to obtain the kinematic and dynamic profiles for the guidance of vehicle. The 8-input dynamic model is developed and applied in an objective function, which is optimized by PSO algorithm to obtain the optimal driving and steering motions for tracking the planned path precisely. The slip angles and lateral forces are also considered in the dynamic model, and the vehicle motion optimization can be implemented in real time. Note that this paper does not address the implementation of the force and steering controllers at the wheels. Simulation results are provided to validate the proposed method.
Dai, P & Katupitiya, J 2014, 'Path planning and force control of a 4WD4WS vehicle', Melbourne.
Dai, P & Katupitiya, J 2014, 'Path planning and tracking of a 4WD4WS vehicle to be driven under force control', 2014 IEEE International Conference on Mechatronics and Automation, IEEE ICMA 2014, pp. 1709-1715.View/Download from: Publisher's site
The aim of this paper is to investigate the possibility of developing a system where forces at the wheels of a ground vehicle are controlled to guide the vehicle along a predetermined path. Any deviations from the desired path is handled using Bézier curve segments that put the vehicle back on track. The Bézier curve segments determine the necessary forces at the wheels. The future aim is to implement independent force control at each of the drive/steering modules of the vehicle. The vehicle is considered to be a rigid body with known inertia and mass. The paper presents path generation using Bézier curves, the extraction of desired forces and the determination of desired steering and propulsion to achieve the desired forces at the wheels of the vehicle. The forces and the control inputs such as the steering angles are then applied to a four wheel driven and four wheel steered vehicle subjected to slip in an open loop setting. Note that this paper does not address the force control issues. Simulation data are generated to validate the proposed methodology. © 2014 IEEE.
Dai, P & Cong, M 2009, 'A study on wafer-handling robot with coaxial twin-shaft magnetic fluid seals', Singapore.